1. Field of the Invention
The present invention relates to a resin binder composition for a non-contact fixing process used for developing electrostatic latent images formed in electrophotography, electrostatic recording method, electrostatic printing, and the like, a toner for a non-contact fixing process comprising the resin binder composition, a developer comprising the toner for a non-contact fixing process, and a method for fixing the toner in a non-contact fixing process.
2. Discussion of the Related Art
A non-contact fixing process includes a process in which light or heat energy is applied to a toner in a non-contacting state, thereby fixing the toner, such as a flash fixing or radiant (oven) fixing process, which has a feature in that the offset phenomenon and the deterioration of resolution, which are often found in contact-fixing, are not found. However, when the light or heat energy is deficient during fixing, the toner cannot be sufficiently melted, so that satisfactory fixing ability cannot be obtained. On the other hand, when the light or heat energy is too intensive, the viscosity of the toner drastically is lowered. When the surface tension acting on the toner exceeds the viscosity, the aggregation and migration of the toner at printed portion take place, so that there is generated a so-called xe2x80x9cvoids,xe2x80x9d which are white voids phenomenon on a fixed image, whereby the photographic density of the image is lowered. Therefore, toners using a specific resin binder are disclosed in Japanese Patent Laid-Open Nos. Hei 8-87130, Hei 5-107805, and the like, in view of eliminating these defects found in the non-contacting fixing process. However, further improvements in the environmental resistance and the storage ability are desired, even though the fixing ability and the void resistance are somewhat improved.
An object of the present invention is to provide a resin binder composition for a non-contact fixing process which effectively prevents the generation of voids in the non-contacting fixing process and is excellent in the environmental resistance and the storage ability as well as in the fixing ability.
Another object of the present invention is to provide a toner for a non-contacting fixing process comprising the resin binder composition, and a developer comprising the toner for a non-contacting fixing process.
Still another object of the present invention is to provide a method for fixing the toner in a non-contact fixing process.
These objects and other objects of the present invention will be apparent from the following description.
The present invention pertains to the following:
[1] a resin binder composition for a non-contact fixing process comprising two or more polyesters having different softening points, wherein each of the polyesters is a resin obtained from an alcohol component consisting essentially of a compound represented by the formula (I): 
xe2x80x83wherein R is an alkylene group having 2 or 3 carbon atoms; each of x and y is a positive number, wherein a sum of x and y is 1 to 16, and wherein at least a polyester having the highest softening point is a cross-linked polyester;
[2] a toner for a non-contact fixing process comprising the resin binder composition as defined above;
[3] a developer comprising the toner as defined above; and
[4] a method for fixing a toner in a non-contact fixing process, comprising applying the toner to a fixing device, wherein the toner comprises the resin binder composition defined above.
The resin binder composition for a non-contact fixing process of the present invention comprises two or more polyesters having different softening points. Since the polyesters having different softening points are contained as mentioned above, the molecular weight distribution of the resin binder composition becomes wider, so that the generation of voids found generally in the non-contacting process can be effectively prevented, whereby the fixing ability can be improved. The resin binder composition of the present invention can be especially preferably used as a resin binder composition for flash fixing process among the non-contact fixing processes such as flash fixing or radiant (oven) fixing processes, from the viewpoint of energy efficiency.
A further great feature of the present invention resides in that all of the polyesters are obtained from an alcohol component consisting essentially of a compound represented by the formula (I): 
wherein R is an alkylene group having 2 or 3 carbon atoms; each of x and y is a positive number, wherein a sum of x and y is 1 to 16, preferably 1.5 to 5.0. Since the compound represented by the formula (I) is used as an alcohol component, a resin having low water-adsorbency is obtained, so that the environmental resistance of the resin is markedly improved. Also, since an aliphatic alcohol is not essentially used, the storage ability is improved. Here, the phrase xe2x80x9cconsisting essentially of a compound represented by the formula (I)xe2x80x9d means that other compounds may be slightly contained in an amount so as not to hinder the object of the present invention.
Therefore, the polyester usable in the present invention, as mentioned above, is obtained by polycondensation of an alcohol component consisting essentially of a compound represented by the formula (I) with a carboxylic acid component. As the carboxylic acid component, dicarboxylic acid compounds may be used for the linear polyesters, and tricarboxylic or higher polycarboxylic acid compounds as well as the dicarboxylic acid compounds may be used for cross-linked polyesters.
The compound represented by the formula (I) includes bisphenol A of an alkylene oxide adduct, each of which has average moles added of 1 to 16, preferably 1.5 to 5.0, such as polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane and polyoxyethylene(2.2)-2,2-bis(4-hydroxyphenyl)propane. These compounds may be used alone or in admixture of two or more kinds.
The dicarboxylic acid compound includes phthalic acid compounds such as phthalic acid, isophthalic acid, and terephthalic acid; fumaric acid; maleic acid; adipic acid; and succinic acid compounds, which may be substituted by an aliphatic hydrocarbon group having 4 to 20 carbon atoms, such as dodecenylsuccinic acid or octylsuccinic acid, preferably substituted by an alkenyl group, acid anhydrides thereof, alkyl (1 to 8 carbon atoms) esters thereof, and the like. Among them, the phthalic acid compounds, the succinic acid compounds, acid anhydrides thereof and alkyl esters thereof are preferable.
The tricarboxylic or higher polycarboxylic acid compound includes trimellitic acid, pyromellitic acid, acid anhydrides thereof, alkyl(1 to 8 carbon atoms) esters thereof, and the like.
In the cross-linked polyester, the tricarboxylic or higher polycarboxylic acid compound is contained in an amount of preferably from 3 to 40% by mol, more preferably from 5 to 25% by mol, of the carboxylic acid component.
The polycondensation of the alcohol component with the carboxylic acid component is carried out, for instance, by the reaction at a temperature of from 180xc2x0 to 250xc2x0 C. in an inert gas atmosphere, using an esterification catalyst as occasion demands.
In the present invention, it is preferable that two or more of the polyesters having different softening points comprise at least one polyester having a softening point of 80xc2x0 C. or more and less than 120xc2x0 C. (low-softening point polyester), and at least one polyester having a softening point of 120xc2x0 C. or more and 160xc2x0 C. or less (high-softening point polyester).
It is desired that the softening point of the low-softening point polyester is 80xc2x0 C. or more and less than 120xc2x0 C., preferably 90xc2x0 C. or more and 110xc2x0 C. or less, and that the softening point of the high-softening point polyester is 120xc2x0 C. or more and 160xc2x0 C. or less, preferably 130xc2x0 C. or more and 153xc2x0 C. or less, from the viewpoints of the fixing ability and the storage ability. In addition, the glass transition temperature of the low-softening point polyester is preferably 50xc2x0 C. or more, more preferably 55xc2x0 C. or more, especially preferably 60xc2x0 C. or more, and from the viewpoint of the storage ability, the glass transition temperature is more preferably 80xc2x0 C. or less. Therefore, the glass transition temperature is preferably from 50xc2x0 to 80xc2x0 C., more preferably from 55xc2x0 to 80xc2x0 C., especially preferably from 60xc2x0 to 80xc2x0 C. Also, the glass transition temperature of the high-softening point polyester is preferably 60xc2x0 C. or more, more preferably from 60xc2x0 to 80xc2x0 C.
The weight ratio of the low-softening point polyester to the high-softening point polyester (low-softening point polyester/high-softening point polyester) is preferably from 20/80 to 90/10, more preferably from 40/60 to 90/10.
As to the polyester usable in the present invention, as long as at least a polyester having the highest softening point is a cross-linked polyester, the remaining polyesters may be either a linear polyester or cross-inked polyester, and it is preferable that only the high-softening point polyester is a cross-linked polyester. When the polyester having the highest softening point is a cross-linked polyester, the void resistance is improved, thereby leading to improvement in the fixing ability.
The toner for a non-contact fixing process of the present invention comprises the resin binder composition of the present invention explained above, which may further comprise in appropriate amounts additives such as a colorant, a charge control agent, a releasing agent, an electric conductivity modifier, an extender, a reinforcing filler such as a fibrous substance, an antioxidant, an anti-aging agent, a fluidity improver, and a cleanability improver.
As the colorants, all of the dyes and pigments which are used as conventional colorants for toners can be used, and the colorant includes carbon blacks, Phthalocyanine Blue, Permanent Brown FG, Brilliant Fast Scarlet, Pigment Green B, Rhodamine-B Base, Solvent Red 49, Solvent Red 146, Solvent Blue 35, quinacridone, carmine 6B, disazoyellow, and the like. These colorants may be used alone or in admixture of two or more kinds. The colorant is contained in an amount of preferably from 1 to 10 parts by weight, based on 100 parts by weight of the resin binder composition.
The toner of the present invention is not particularly limited, and includes pulverized toners, polymerization toners, encapsulated toners, and the like, preferably a pulverized toner obtained by kneading and pulverization method. As a general method, for instance, a resin binder, a colorant, and the like are homogeneously blended in a mixer such as a ball-mill, and thereafter the mixture is melt-kneaded by a seal-type kneader or a single-screw or twin-screw extruder, or the like, and the kneaded mixture is cooled, pulverized, and classified. Further, a fluidity improver or the like may be added to the toner surface as occasion demands. It is preferable that the toner obtained as described above has a weight-average particle size of from 3 to 15 xcexcm.
The toner for a non-contact fixing process of the present invention may be used alone as a developer when a magnetite particulate is contained, or as a nonmagnetic one-component developer when a fine magnetite particulate is not contained, or as a two-component developer by mixing the toner with a carrier.
This toner can be suitably used for a fixing device utilizing a non-contact fixing process. The present invention also provides a method for fixing a toner utilizing the non-contact fixing process, preferably a flash fixing process.